diff --git a/modules/base.nix b/modules/base.nix
index ef88b49..0a7c91d 100644
--- a/modules/base.nix
+++ b/modules/base.nix
@@ -36,6 +36,8 @@
     extraGroups = [ "networkmanager" ];
   };
 
+  # Optimise nix store during every build. This may slow down builds.
+  # https://nixos.wiki/wiki/Storage_optimization
   nix.settings.auto-optimise-store = true;
 
   # Firewall.